Bitumen products (also known as asphalts), tars or resins are well known materials used in many road building, construction, and other industrial applications. The characteristic that bitumen products have in common is that they are solid or semi-solid at ambient temperature and liquid at elevated temperatures. For transportation from source to end-use location, these materials are either carried in bulk or in containers. When carried in bulk, they should be maintained at such a temperature that their viscosity is low enough to allow for easy pumping and transfer thereof. When carried in containers, such as drums or pails of any size and shape, their temperature, after filling, drops to ambient and the product becomes solid or semi-solid. The containers are generally transported and stored at ambient temperature. Before use, the containers and the material they contain have to be heated-up or melted to allow for the pouring, pumping and transfer of the product. After heating, the container usually cannot be reused and must be disposed of.
Bitumen product containers have to be solid enough for handling and transport, and have to be able to be heated up before the product can be used. For this purpose, they are usually made of metal, most commonly steel, and are in the form of drums. The main advantage of steel drums, compared with other types of similar packaging, is that they are relatively inexpensive. There are, however, at least three problems associated with using drum containers. The first is that the drum containers have to be disposed of after use. As they contain bitumen product, it is almost impossible to clean them up for re-use and they therefore become waste. The second is that, owing to the relatively high viscosity of bitumen products, it is practically impossible to empty the drums totally. As a result, it is usually considered that up to 2 to 3% of the product left adhering to the walls of the container is lost. This increases the amount of wastage material released into the environment. The third problem relates to transport cost and efficiency. Due to the loss of usable amount of bitumen products through its adherence to the container walls, this results in the need for an overestimation in the actual and final useable weight of bitumen products. Accordingly, to make up for the shortfall of useable bitumen one has to increase the volume of product ordered, which increases the total weight of product required to be transported.
To solve the problem of wastage and freight burden, a number of solutions have been proposed, and a number of them utilizing soft bag packaging as the container. In these cases, the bitumen product is packed, while hot, into soft bags. Upon cooling down, the bitumen product becomes solid or semi-solid at ambient temperature, as does the whole of the package. Bags can then be handled, stored, transported to the end-use location with freight burden kept to minimum. The use of a polypropylene film to package roofing asphalt has also been described (see U.S. Pat. No. 5,452,800).
While the solution of using plastic bagging or film addresses one of the problems associated with steel drum packaging, it is in itself a source for other problems. The two main reasons relate to the density and then to the compatibility of the container material with the bitumen contained therein. As mentioned, bitumen products are required to be molten before transfer and use. The plastic in contact with the bitumen product cannot be removed, as it is firmly adhered to the outside of the product. In order to access the bitumen product, it therefore has to be melted together with its packaging.
The plastic is usually designed to melt at the melting temperature of the bitumen product. However, this does not necessarily mean that the plastic is compatible with the bitumen product. Plastic or polymer products, such as those used in the packaging industry, like polyethylene, polypropylene, polystyrene, etc., are not easily dispersed in bitumen products. Not only does it take quite a lot of shearing energy to achieve dispersion, but it also requires the materials to be chemically compatible with each other. As a result of incomplete dispersion throughout the bitumen product, and due to the lower density of the plastic or polymer materials compared with that of bitumen, the plastic materials like polyethylene, polypropylene, and polystyrene migrate towards the surface of the melting or molten bitumen material. Over time, a film, or skin, of the plastic material so formed thickens and rapidly becomes a source for severe operational problems. Interestingly, however, the formation of this film has been viewed as a beneficial outcome in that it is able to reduce the emission of fumes from asphalt materials during the melting process (see U.S. Pat. Nos. 5,733,616; 5,989,662; and 6,107,373, which, in addition to describing the use of solid containers that melt with asphalt, even describe the intentional addition of polymer material to molten asphalt to form a skin to reduce fumes). See also WO 00/55280.
However, road-paving bitumens, having a significantly lower softening point, are much softer than roofing bitumens. Road-paving bitumens are therefore used and handled at significantly lower temperatures in such a way that fumes generated during storage is of much less concern that with roofing bitumens. In addition, roofing bitumen is heated up on site and used in relatively small quantities, whereas road-paving bitumen is used in much larger quantities and stored in tanks of considerable size. A skin of polymer materials generated by the packaging materials for bitumens, as described above, would be undesirable in most cases of road paving bitumen melting and storage. The high viscosity and low density of such a polymer skin would make it very difficult to remove or to consume. The skin would also arguably increase in thickness at the surface of a tank or other container with each load and over time, become too thick and therefore impossible to remove. Additionally, road-paving bitumens, unlike roofing bitumens, still flow at ambient temperature. This makes them more difficult to package in suitable packaging material than roofing bitumen.
In order to reduce the problem of polymer skin formation at the surface of the molten bitumen material, several options have been proposed like reduced packaging thickness or the use of double layer packaging. In the case where the packaging material is kept thin, such packaging becomes sensitive to puncturing and damage during transport. This, in turn, results in leaks with all the associated spillage problems. As a result, the main container containing bags of bitumen products in thin bags can be badly dirtied and a large part of the cargo can be spoiled with bags being glued to each other. Also, and in the case of double layer packaging, the outer layer has to first be peeled off and disposed of before the melting process can take place. Peeling off the outer layer can prove to be very difficult due to the thinness of the inner layer, which frequently results in leakage of small amounts of bitumen product into the space between the outer and inner layers. This makes the peeling off of the outer layer impossible in extreme cases. This results in more packaging (from the thicker outer layer) accumulation at the surface of the molten bitumen, causing associated operational problems, like product homogeneity, pumping, pipe clogging, etc.
Modification of the characteristics of bitumen products by the addition of polymers or plastic components is a well-known field of technology and this has been described and discussed in many publications, at international conferences, and in the internal publications of several corporations. In the field of bitumen technology, and as reported in publications from the ASTM and the European Asphalt Pavement Association, it is today widely accepted that polymers and plastic do not readily blend with bitumen products, and that a mixing process using shearing energy and compatibilization time is required before all the components form an intimate blend.
Citation of the above documents is not intended as an admission that any of the foregoing is pertinent prior art. All statements as to the date or representation as to the contents of these documents is based on the information available to the applicant and does not constitute any admission as to the correctness of the dates or contents of these documents.